Abstract: A gauge for testing guards on machines against safety standards setting minimum clearances to moving parts as a relation of the openings in the guard. The gauge is in the form of a shaft having sized ends on either end thereof related to designated gauge opening sizes. Stop collars are positioned on the shaft at fixed lengths from the respective ends such that if the end passes through the opening the stop collar must contact the guard prior to the end touching any moving part within the guard in order for the guard to be in compliance. Additionally, the stop collars are sized to allow testing of additional openings to determine the size thereof. Thus, both the sized ends and the stop collars can be used to chuck opening sizes.